Acid primary cells



1 fluoride ion as an electrolyte additive.

is less important.

United States Patent This invention relates to primarycellshavingtitaniumcontaining anodes, and phosphoric acid electrolytes. Theanodes comprise alloys containing at least 50 atomic percent titanium.The cathodes may comprise any suitable polarizers, lead dioxide beingprimary cell systems described here. The original acid preferred for thephosphoric acid electrolytes provides still higher voltages, higherrates oi energy output per unit weightorper unit area, and higher totalenergy outputs.

These advantages are important, as high work ng V9112? age under load,maximum discharge rate from a fixed cell size, and total cell capacityatuseful wattages are factors emphasized in the primary cell trade.

Table 1, below, lists properties of two typical titanium alloy anodes inconcentrated electrolytes, showing that (A) The phosphoric acid cellshave higher voltages the comparable alkaline cell. (B) The cell voltageand the available anode current densities for the Ti-=-27 Mol0 Al alloycell are greater in 85 percent H 1 0 than in H P O (C) The Ti-Mo-Alalloy provides greater voltages and higher anode current densities inthe 85 percent phosphoric acid than the Ti-M'o-Nb alloy.

Table 1. Titanium alloy electrodes in electrolytes without additivesAlloy Anode Compo- Anode Discharge Properties, Closed Circuit Voltage,Volts vs. P1102 at Anode Current Es mp s sition. weight percentElectrolyte De s ty. na-{ n} Zero 0. 01 0. 02 0. 10

Tl- 27 Mo-lO AL..." Pyrophosphoric Acid, H4P2O1 1. 50 1.35 1. 23

(equivalent to 119" weight percent HgPOl).

T1127, M9 110 AL"..- 85 weight, percent H 204 l. 90 1. 7- 1.5

, Ti -.27 Moe-10 Nb"... 55 percent KOH 1 1.10 1 1.00 0.915

I Volts vs. HgO depolari'zer.

electrolyte may be any form of phosphoric acid, 'hypo-, meta-, ortho-,or pyro-, or phosphorus penta-oxide. The composition of the aqueoussolution depends upon the relative concentrations of hydrogen,phosphorus, and oxygen atoms, regardless of the original form of theacid placed in the water. For convenience herein, concentrations arespecified as weight percentages of ortho-phosphoric acid, H PO in water.It is understood, however, that any convenient starting materials may beused to obtain the specified concentrations. The useful range ofortho-phosphoric acid concentration is 3 0 to 100 weight percent. Thepreferred concentration range is 30 to 85 weight percent orthophosphoricacid. The phosphoric acid may also contain The fluoride ion can be usedas an additive in all of the phosphoric acid concentrations within theuseful range. However, 30 to 85- weight percent is also the preferredortho-phosphoric acid concentration for use with the fluoride additive.

Typical anodes for use in these electrolytes are Ti-2;7 Mol0 Al and Ti27Mo-l0 :Nb (where not otherwise specified, numbers indicate weightpercent). The aluminum-containing alloy provides high rate of dischargein a given electrolyte, where cell life is less important. The;niobium-containing alloy provides long cell life in a given electrolytewhere high rate of discharge The alloy Ti3i), Mo may also be used forlong cell life.

A unique feature of this invention is that the fluoride additive is notconsumed electrochemically during cell discharge.

Primary cells according to this invention provide higher voltages thanthose of alkaline primary cells using titanium-containin-g anodes.Phosphoric acid cells using Ti--27 Mo-l0 Nb anodes provide 10 to 50percent higher voltages than alkaline cells using the same anode. (SecTables I and HI.) The addition of fluoride to the ingredient in anygiven Table 11, below, lists properties of the "rt-27 Al alloy anode indifierent concentrations of phosphoric acid with all of the electrolytescontaining 0.2; molar fluori i n.- Th ta sh wincrea ed vo tag creas d avila l a o e curr n d n i y w th d con ent ion o H3 O he on ntration ge39 to p r n prov des high r o tages and hig sciat c ing anode currentdensities. The addit oi (E). 'o the electr lyte in reases the voltage,under loa app rent from a comparison of ETampl 5 (Table 11) with Example1 (Table I). a of Ex mpl 7 (Table 11') with. Examp e 2 (Table,

Tablev II.-Ti:-' 27 M 0-1 0 Al anode in phosphoric acids containing 0.2molar fluoride ion Table III, below, shows that the Pi-27 M0410 anode ismore corrosion resistant than the the Ti-27 Mo-lO Al anode in 50 weightpercent phosphoric acid containing about 0.2 M (F)-. This electrolytewas the most corrosive of those tested, yet no corrosion was observed atthe Ti-27 Mo-10 Nb anode. These facts mean that long cell shelf life isobtained with the Ti-27 Mo-10 Nb cell; while the Ti-27 -Mo10 Al cell,having shorter shelf-life provides higher voltages.

se t.

Table III.Comparison of titanium alloy anodes Ti-27 Mo-l Al Tl-27 Mo- NbTi-27 M0-10 Nb in 50% HaPO4+ in 50% H1PO4+ in 55% KOH 0 en CircuitVoltage, volts 1.92 1.54 1.1. C Brad ('Jircuit Voltage, volts at AnodeCurrent ens I 0.01 maJin. 1.0.

0.10 maiiimtu 0.05. a 1.0 ma./ 1.89- 1.0-.- 0.85. Corrosion at Anodevigorous evolving no gas evolutlon. no gas evolution.

1 gas.

1 Volts versus a lead dioxide depolarlzer. 1 Volts versus a mercuricoxide depolarlzer.

Table IV, below, shows that the addition of 0.2 molar fluoride ion to 85percent phosphoric acid provides the following improvements for a1.6-gram sintered Ti-27 Mo.10 Al anode.

(1) The cell voltage is increased about 0.1 to 0.6 volt, depending onthe load.

7 (2) The discharge rate is increased about 2 to 4 times.

(3) The total energy output for a given anode weight or area isincreased by two to several times.

1 In the absence of (F)-, the sinter polarized to 0.975 volt by another7 minutes at 4 mllliamperes. The current was changed to 2 rnilhamperesand the voltage rose to about 1.1 volts by 29 minutes.

Another test with a second 1.6 gram Ti-27 Mo-10 Al sinter indicated that2 milliamperes is about the highest current obtainable for an extendedtime in 85 percent H3PO4. With this sinter, complete polarizationoccurred in about 5 minutes at 4 milliamperes, but the voltage atZmilliamperes was steady at 1.19 volts for about 16 hours. On the otherhand, the first sinter provided a steady. 1.17 volts at 4 milliamperesfor 16 hours in the 85 percent H PO with (F) present.

The fluoride ion is not consumed electrochemically during celldischarge. The sinter was discharged a total of about 43 ampere minutesin the 85 percent H PO containing only the equivalent of about 8.1ampere minutes of fluoride. Discharge rates of 3 to 4 milliarnperes weremaintained for 16 hour periods per day for 12 days. If the fluoride ionhad been consumed the anode would have polarized.

No improvement is observed when the fluoride concentration' is as low asabout 0.02 molar. At least about 0.05 M fluoride ion is necessary toactivate the titanium alloy anode. The preferred range for fluorideconcentration is from about 0.05 to 0.2 molar; but higher concentrationsup to saturation of the phosphoric acid with fluoride salt may be usedfor larger rates of discharge.

' anode consisting essentially of at least atomic percent titanium, theremainder being essentially molybdenum and a'material of the'groupconsisting of aluminum and niobium, and an electrolyte consistingessentially of an aqueous solution of from about 30 to 85 weight percentortho-phosphoric acid.

3. A primary cell comprising a cathode, an alloy anode consistingessentially of at least 50 atomic percent titanium, the remainder beingessentially molybdenum and a material of the group consisting ofaluminum and niobium, and an electrolyte consisting essentially of anaqueous solution of about 50 weight percent ortho-phosphoric acid.

.4. A primary cell comprising a cathode, an alloy anode consistingessentially of at least 50 atomic percent titanium, the remainder beingessentially molybdenum and a material of the group consisting ofaluminum and niobium, and an electrolyte consisting essentially of another fluoride salts.

aqueous solution of from about 30 to 100 weight percent ortho-phosphoricacid and from about 0.05 to 0.2 molar fluoride ion. I

-5. A primary cell comprising a cathode, an alloy anode consistingessentially of at least 50 atomic percent titanium, the remainder beingessentially molybdenum and a material ofthe group consisting of aluminumand n1 obium, andan electrolyte consisting essentially of an aqueoussolution of from about 30 to weight percent ortho-phosphoric acid andfrom about 0.05 to 0.2-molar fluoride ion.

6. A primary cell comprising a cathode, an alloy anode consistingessentially of at least 50 atomic percent titanium, the remainder beingessentially molybdenum and a material of. the group consistingofaluminum, andniobium, and an electrolyte consisting essentially of anaqueous solution of about 50 weight percent ortho-phosphoric acid and.from about 0.05 to 0.2 molar fluoride ion.

References Cited in the file of thispatent, UNITED STATES PATENTSv 7717,108 Morrison' Dec.30, 1902 1,748,485 Kugel Feb. 25, 1930 Fox Mar.10, 1953

1. A PRIMARY CELL COMPRISING A CATHODE, AN ALLOY ANODE CONSISTINGESSENTIALLY OF AT LEAST 50 ATOMIC PERCENT TITAMIUM, THE REMAINDER BEINGESSENTIALLY MOLYBDENUM AND A MATERIAL OF THE GROUP CONSISTING OFALUMINUM AND MIOBIUM, AND AN ELECTROLYTE CONSISTING ESSENTIALLY OF ANAQUEOUS SOLUTION OF FROM ABOUT 30 TO 100 WEIGHT PERCENT ORTHO-PHOSPHORICACID.